Evaluation of in vitro spectra of activity of azithromycin, clarithromycin, and erythromycin tested against strains of Neisseria gonorrhoeae by reference agar dilution, disk diffusion, and Etest methods.

The macrolide-azilide susceptibility testing (agar dilution, disk diffusion, Etest) criteria for 105 Neisseria gonorrhoeae strains were evaluated. In addition, the potencies of azithromycin, clarithromycin, and erythromycin were studied. The most active macrolide-azilide agent was azithromycin (MIC at which 90% of the isolates are inhibited [MIC90], 0.5 microgram/ml) compared with clarithromycin (MIC90, 1.5 to 2 micrograms/ml) and erythromycin (MIC90, 2 to 4 micrograms/ml). The Etest (AB Biodisk, Solna, Sweden) was observed to produce MIC results very similar to those of the reference agar dilution test (GC agar base), with 100% of the results within 1 log2 dilution step of the reference MICs. The disk diffusion test zone diameters for all three drugs correlated at an acceptable level (r = -0.81 to -0.92) with the reference agar dilution MICs. Interpretive criteria for susceptibility were proposed for azithromycin at a MIC of < or = 2 micrograms/ml and a disk diffusion test zone of > or = 25 mm. No category for resistance was proposed because of the paucity of strains for which MICs were > 2 micrograms/ml. These tentative criteria should be further validated by correlations with clinical trial data for gonococcal strains (as they emerge) that have azithromycin MICs above the proposed susceptible category range.     

Metronidazole susceptibility testing for Helicobacter pylori: comparison of disk, broth, and agar dilution methods and their clinical relevance.

Since the methods for metronidazole susceptibility testing of Helicobacter pylori have not been standardized or validated, we compared three methods that are used to test the metronidazole susceptibilities of 25 isolates of H. pylori. Specifically, we examined the methods of Steer's replicator agar dilution, tube broth microdilution, and modified Kirby-Bauer disk diffusion. The metronidazole disk zone sizes obtained by the disk diffusion method correlated well (r = 0.74) with the MICs obtained by the agar dilution method. Afterward, the disk diffusion method was used to characterize the metronidazole susceptibilities of 44 isolates of H. pylori. Dual therapy (bismuth and metronidazole) proved to be highly effective against metronidazole-susceptible strains (81.6% eradication rate) but fared poorly against resistant strains (16.7% eradication rate; P < 0.01). Using agar dilution testing, we validated the modified Kirby-Bauer disk diffusion method for metronidazole susceptibility testing of H. pylori and conclude that it is practical, accurate, and clinically applicable.     

Assessment of metronidazole susceptibility in Helicobacter pylori: statistical validation and error rate analysis of breakpoints determined by the disk diffusion test

Metronidazole susceptibility of 100 Helicobacter pylori strains was assessed by determining the inhibition zone diameters by disk diffusion test and the MICs by agar dilution and PDM Epsilometer test (E test). Linear regression analysis was performed, allowing the definition of significant linear relations, and revealed correlations of disk diffusion results with both E-test and agar dilution results (r2 = 0.88 and 0.81, respectively). No significant differences (P = 0.84) were found between MICs defined by E test and those defined by agar dilution, taken as a standard. Reproducibility comparison between E-test and disk diffusion tests showed that they are equivalent and with good precision. Two interpretative susceptibility schemes (with or without an intermediate class) were compared by an interpretative error rate analysis method. The susceptibility classification scheme that included the intermediate category was retained, and breakpoints were assessed for diffusion assay with 5-microg metronidazole disks. Strains with inhibition zone diameters less than 16 mm were defined as resistant (MIC > 8 microg/ml), those with zone diameters equal to or greater than 16 mm but less than 21 mm were considered intermediate (4 microg/ml < MIC 相似文献   

Tentative criteria for confirming the in vitro susceptibilities of Haemophilus influenzae and Neisseria gonorrhoeae to two fluoroquinolones (sparfloxacin and levofloxacin), including quality control parameters.

Sparfloxacin and levofloxacin were evaluated against 150 Haemophilus influenzae isolates and 149 Neisseria gonorrhoeae isolates in order to define susceptibility testing parameters. Sparfloxacin-susceptible H. influenzae strains were defined as those for which the MICs were < or = 0.25 microgram/ml and the zones were > or = 30 mm, and N. gonorrhoeae susceptible strains were those for which the MICs were < or = 0.03 microgram/ml and the zones were > or = 39 mm (5-micrograms disks). Levofloxacin-susceptible strains of H. influenzae included those for which the MICs were < or = 0.12 microgram/ml and the zones were > or = 32 mm and N. gonorrhoeae susceptible strains were those for which the MICs were < or = 0.12 microgram/ml and the zones were > or = 37 mm (5-micrograms disks). Criteria for a resistant category cannot yet be defined for either quinolone. In multilaboratory studies with different lots of Haemophilus Test Medium, replicate tests with the standard control strain of H. influenzae (ATCC 49247) were evaluated. For sparfloxacin disk tests, the proposed zone size limits were 33 to 42 mm and broth microdilution MIC limits were 0.004 to 0.016 microgram/ml, whereas for levofloxacin tests, zone size limits were 32 to 41 mm and broth microdilution MIC limits were 0.008 to 0.03 microgram/ml. Other multilaboratory studies evaluated tests with supplemented GC agar and N. gonorrhoeae ATCC 49226; for both drugs, zone size limits were 44 to 52 mm and agar dilution MIC limits were 0.004 to 0.016 microgram/ml.     

Rapid method for determining antimicrobial susceptibility of Haemophilus influenzae.

A method was developed to determine the susceptibility of Haemophilus influenzae to ampicillin, cefamandole, and chloramphenicol by using the MS-2 system (Abbott Laboratories) for determining minimum inhibitory concentrations (MIC). The MS-2 results for 132 strains of H. influenzae were compared with the results of agar disk diffusion, agar dilution, and beta-lactamase tests. Twenty-four strains (18.2%) of H. influenzae were resistant to ampicillin by the agar dilution method, as opposed to 25 strains by the MS-2 method. For a beta-lactamase-negative strain, the agar dilution MIC was 4 micrograms/ml, and the MS-2 MIC was 16 micrograms/ml. Twenty-one strains produced beta-lactamase; two beta-lactamase-negative strains were resistant by MS-2, agar dilution, and agar disk diffusion. In addition, one beta-lactamase-negative strain, for which the agar dilution MIC was 32 micrograms/ml and the MS-2 MIC was 16 micrograms/ml, was sensitive by agar disk diffusion. Overall, the MS-2 method compared favorably with the agar dilution method for determining the MIC of ampicillin, cefamandole, and chloramphenicol for H. influenzae.     

Validation of diffusion methods for macrolide susceptibility testing of Helicobacter pylori

Helicobacter pylori resistance to macrolides is increasing, and the need for susceptibility testing has become crucial. The only standardized method is agar dilution, which is not adapted to clinical practice. The present work aimed: (1) to optimize the technical conditions and to assess the reproducibility of the E-test and disk diffusion method for macrolides susceptibility testing of H. pylori, and (2) to assess the performances of these two phenotypic methods in detecting strains harboring a resistance mechanism to macrolides. We used 191 isolates collected in nine centers of France and Belgium. Phenotypic tests were performed on Mueller-Hinton agar supplemented with 10% horse blood, inoculated with a 2-day-old H. pylori suspension (10(8) CFU/ml), and incubated for 72 hr at 37 degrees C under microaerophilic conditions. The reproducibility studied on two randomly selected strains was better for disk diffusion than for the E-test for both clarithromycin and erythromycin. For a subset of 10 strains, the MICs of erythromycin and clarithromycin did not differ from more than one two-fold dilution when determined by E-test or agar dilution method. The breakpoints were for MICs: 1 mg/L for both clarithromycin and erythromycin and for inhibition diameters, 22 mm for clarithromycin and 17 mm for erythromycin. There was a 100% concordance between susceptibility to erythromycin and clarithromycin. However, the susceptible and resistant populations were better separated by testing erythromycin. Of 34 resistant strains, two lacked the A2142G and A2143G point mutations in 23S rRNA by PCR-RFLP. None of 15 tested sensitive strains were positive for one of these two point mutations. For clinical practice, we recommend to assess macrolide susceptibility of H. pylori by using one of these two phenotypic methods under the described technical conditions.     

Role of screening agar plates for in vitro susceptibility testing of Helicobacter pylori in a routine laboratory setting

BACKGROUND: Resistance of Helicobacter pylori to the more frequently used antibiotics (metronidazole and clarithromycin) reduces eradication rates even with triple treatment. Determining the antibiogram profile of H pylori can take up to 14 days and delays appropriate treatment. AIMS: To determine the role of screening agar plates for more rapid in vitro susceptibility of H pylori to metronidazole, amoxicillin, and clarithromycin. METHODS: Routine gastric biopsy specimens from 507 dyspeptic patients were inoculated on to 10% lysed blood agar plates containing metronidazole (8 microg/ml), clarithromycin (2 microg/ml), or amoxicillin (0.5 microg/ml). The minimum inhibitory concentration (MIC) of the 90 isolates was determined using the E test. RESULTS: Metronidazole resistance was detected in 28 of 90 isolates by E test and nine of 98 by screening agar. The screening agar detected none of the four clarithromycin resistant isolates detected by the E test. CONCLUSIONS: The screening agar method is not sufficiently sensitive to be used alone.     

Detection of quinolone-resistant Neisseria gonorrhoeae.

The present National Committee for Clinical Laboratory Standards (NCCLS) guideline for testing Neisseria gonorrhoeae quinolone susceptibility defines only a susceptible category for ciprofloxacin, enoxacin, lomefloxacin, and ofloxacin, while susceptible, intermediate, and resistant categories are defined for fleroxacin. To further define the criteria for detection of quinolone resistance in gonococci, by standard disk diffusion and agar dilution methodologies recommended by the NCCLS, we tested 29 strains of quinolone-resistant N. gonorrhoeae (QRNG) recently isolated from ofloxacin-treated patients who were considered clinical failures. Regression analyses were performed on these results together with those of another 20 strains showing reduced susceptibility and 13 fully susceptible strains (ofloxacin MICs of < or = 0.25 microgram/ml). With 5-micrograms ofloxacin disks, resistance in 27 (93.1%) of the QRNG strains (MICs of > 1 microgram/ml) was detected by the criterion of a zone diameter of < 22 mm, while in the remaining 2 (6.9%), the disks failed to detect resistance. A cluster of 15 highly resistant strains showed ofloxacin MICs of > 4 micrograms/ml and zone diameters of < 13 mm. When tested with 5-micrograms ciprofloxacin disks, the corresponding values for resistance and high-level resistance of these QRNG strains were < 25 mm (MICs of > 0.5 micrograms/ml) and < 15 mm (MICs of > 2 micrograms /ml), respectively. Six strains for which ofloxacin MICs were > or = 8 micrograms/ml showed no zones at all with both 5-micrograms ofloxacin and 5-micrograms ciprofloxacin disks. These QRNG strains are now firmly established in the Southeast Asia region, and it is important for clinical laboratories to recognize these clinically resistant strains and to monitor their spread.     

Development of interpretive criteria and quality control limits for macrolide and clindamycin susceptibility testing of Streptococcus pneumoniae.

A six-laboratory collaborative study was conducted to develop MIC and zone diameter quality control limits and interpretive criteria for antimicrobial susceptibility testing of Streptococcus pneumoniae with azithromycin, clarithromycin, dirithromycin, and clindamycin. The MICs of all of the agents plus erythromycin for 302 clinical isolates of pneumococci that had been selected with an emphasis on resistant strains were determined by use of the National Committee for Clinical Laboratory Standards (NCCLS)-recommended broth microdilution procedure. The zone diameters of the isolates were also determined for the same agents except erythromycin by the NCCLS disk diffusion test procedure. Repeated testing of S. pneumoniae ATCC 49619 with different sources and lots of media and disks allowed development of MIC and zone diameter quality control ranges for these agents. Interpretive criteria for the MIC of azithromycin were established and were as follows: susceptible, < or = 0.5 microgram/ml; intermediate, 1 microgram/ml; and resistant, > or = 2 micrograms/ml. The interpretive criteria advocated for the MICs of clarithromycin and clindamycin were as follows: susceptible, < or = 0.25 microgram/ml; intermediate, 0.5 microgram/ml; and resistant, > or = 1 microgram/ml. Comparison of MICs and disk diffusion zone diameters led to the development of interpretive criteria for the zone diameters for azithromycin, clarithromycin, and clindamycin that correlated well with these MIC breakpoints. Testing of this organism collection also led to the reestablishment of the erythromycin MIC breakpoints as being identical to those of clarithromycin, which resulted in equivalent cross-susceptibility and cross-resistance for the three macrolides that are currently marketed in the United States. Thus, the susceptibility of pneumococci to azithromycin and clarithromycin can be predicted accurately by testing only erythromycin in clinical laboratories. This recommendation, as well as the interpretive and quality control criteria that are described, have been accepted by NCCLS and are included in the latest NCCLS susceptibility testing guidelines.     

Comparative evaluation of macrodilution and chromogenic agar screening for determining fluconazole susceptibility of Candida albicans.

A simple screening method for fluconazole susceptibility using CHROMagar Candida with fluconazole was compared with the National Committee for Clinical Laboratory Standards (NCCLS) macrobroth method. In this agar dilution method, susceptible Candida albicans colonies are smaller on medium with fluconazole than on fluconazole-free medium. Yeasts with decreased susceptibility have normal-sized colonies on medium containing fluconazole. On agar with 16 micrograms of fluconazole per ml, 32 of 34 strains with NCCLS MICs of > or = 16 micrograms/ml were correctly predicted, as were 66 of 68 with MICs of < 16, an agreement of 96%. On agar with 8 micrograms of fluconazole per ml, 38 of 41 isolates with MICs of > or = 8 were correctly predicted, as were 59 of 61 isolates with MICs of < 8, an agreement of 95%. This agar dilution methods appears to highly correlate with NCCLS macrobroth methods for detection of C. albicans and may be an effective screen for fluconazole susceptibility.     

Simple method for detecting fluconazole-resistant yeasts with chromogenic agar.

A method for detecting fluconazole-resistant yeasts was developed that uses chromogenic agar containing fluconazole. Yeasts were plated on media with fluconazole at 0, 8, and 16 micrograms/ml. On media without fluconazole, normal growth of susceptible yeasts (defined as those having a fluconazole MIC of < 8 micrograms/ml) was detected, while fluconazole-containing media suppressed susceptible strains and normal colonies of resistant yeasts (fluconazole MICs of > or = 8 micrograms/ml) were detected. This method was used to screen for resistance in oropharyngeal candidiasis. Isolates having fluconazole MICs of > or = 8 micrograms/ml and < 8 micrograms/ml were correctly predicted in 43 of 45 cultures and 115 of 116 cultures, respectively. This screening method appears to be rapid and sensitive for detection of fluconazole-resistant yeasts.     

In vitro susceptibility ofHelicobacter pylori to trospectomycin,pirlimycin (U-57930E), mirincamycin (U-24729A) and N-demethyl clindamycin (U-26767A)

The in vitro activity of trospectomycin, pirlimycin, mirincamycin and N-demethyl clindamycin was measured against 46 clinical isolates ofHelicobacter pylori using an agar dilution technique. The MIC50 and MIC90 were 4 and 64 µg/ml for pirlimycin and N-demethyl clindamycin, and 32 and 128 µg/ml for mirincamycin, respectively. All 46 strains were sensitive to trospectomycin with an MIC50 of 8 µg/ml and an MIC90 of 16 µg/ml. Of seven strains with the highest trospectomycin MICs (8 or 16 µg/ml) 100 % were found to be resistant to metronidazole. Among ten strains with low trospectomycin MICs (2 µg/ml or less) 100 % were sensitive to metronidazole. Possible explanations for the apparent correlation between the MICs of the two drugs are discussed. Since all metronidazole resistant strains were sensitive to trospectomycin, this drug may be useful in treating infection with metronidazole resistantHelicobacter pylori.     

Oxyrase, a method which avoids CO2 in the incubation atmosphere for anaerobic susceptibility testing of antibiotics affected by CO2.

The Oxyrase agar dilution method, with exclusion of CO2 from the environment, was compared with the reference agar dilution method recommended by the National Committee for Clinical Laboratory Standards (anaerobic chamber with 10% CO2) to test the susceptibility of 51 gram-negative and 43 gram-positive anaerobes to azithromycin and erythromycin. With the Oxyrase method, anaerobiosis was achieved by incorporation of the O2-binding enzyme Oxyrase in addition to susceptibility test medium, antibiotic, and enzyme substrates into the upper level of a biplate. Plates were covered with a Brewer lid and incubated in ambient air. With azithromycin, Oxyrase yielded an MIC for 50% of strains tested (MIC50) and MIC90 of 2.0 and 8.0 micrograms/ml, compared to 8.0 and > 32.0 micrograms/ml in standard anaerobic conditions. At a breakpoint of 8.0 micrograms/ml, 90.4% of strains were susceptible to azithromycin with Oxyrase, compared to 53.2% in the chamber. The corresponding erythromycin MIC50 and MIC90 were 1.0 and 8.0 micrograms/ml with Oxyrase, compared to 4.0 and > 32.0 micrograms/ml by the reference method, with 89.3% of strains susceptible at a breakpoint of 4 micrograms/ml with Oxyrase, compared to 60.6% in CO2. Exclusion of CO2 from the anaerobic atmosphere when testing for susceptibility to azalides and macrolides yielded lower MICs, which may lead to a reconsideration of the role played by these compounds in treatment of infections caused by these strains.     

Antimicrobial Susceptibility of Helicobacter pylori Determined by the E Test Using Tetrazolium Egg Yolk Agar

Metronidazole and tetracycline E tests were compared to an agar dilution method for the antimicrobial susceptibility testing of Helicobacter pylori. Sixteen strains were tested by using tetrazolium egg yolk (TEY) agar. The characteristic E test inhibition ellipse was clearer on TEY agar than on standard blood agar and gave results comparable to those of the agar dilution test. The use of TEY medium is preferable to that of blood agar medium in E test MIC determinations for H. pylori.     

Interpretive criteria and quality control parameters for testing of susceptibilities of Haemophilus influenzae and Streptococcus pneumoniae to trimethoprim and trimethoprim-sulfamethoxazole. The Antimicrobial Susceptibility Testing OC Group.

Two hundred twenty-eight strains of Haemophilus influenzae and 234 strains of Streptococcus pneumoniae were tested by broth microdilution and disk diffusion methods for susceptibility to trimethoprim (TMP) and TMP-sulfamethoxazole (SMX) to evaluate proposed criteria. Data are presented to support the proposed TMP MIC breakpoints of < or = 2.0 micrograms/ml for susceptibility and > or = 4.0 micrograms/ml for resistance for both species and TMP-SMX MIC breakpoints of < or = 2.0-38 micrograms/ml for susceptibility and > or = 4.0-76 micrograms/ml for resistance. Corresponding zone diameter breakpoints for H. influenzae for both drugs are proposed: < or = 10 mm = resistant; > or = 16 mm = susceptible. A 10-laboratory study documented reproducibility of such tests with standard control strains. The following control limits are proposed for tests of H. influenzae ATCC 49247 against TMP; MIC, 0.12 to 0.5 microgram/ml; zone diameter, 27 to 33 mm. The current limits for TMP-SMX were confirmed. For tests of S. pneumoniae ATCC 49619, MICs of TMP were 1.0 to 4.0 micrograms/ml and the current TMP-SMX MIC range was confirmed. Disk susceptibility tests of either drug against pneumococci were not reproducible, and consequently neither quality control limits nor interpretive criteria could be established. Endpoint interpretation and lot-to-lot variability in Mueller-Hinton agars were significant factors leading to interlaboratory variability.     

In vitro activity of fosfomycin alone and in combination with amoxicillin, clarithromycin and metronidazole against Helicobacter pylori compared with combined clarithromycin and metronidazole

In order to evaluate the suitability of fosfomycin in combination with other agents for the treatment of Helicobacter pylori infections, the susceptibility profiles of 65 H. pylori strains were determined against multiple antimicrobial agents and combinations thereof using the agar dilution method. For fosfomycin alone, the range of minimum inhibitory concentration (MIC) results and the MICs at which 50% and 90% of strains were inhibited were 0.5–32 g/ml and 2 and 4 g/ml, respectively. For the combination of fosfomycin with amoxicillin, clarithromycin or metronidazole, the means calculated for the minimum and maximum fractional inhibitory concentration index were 0.70–1.17 and 1.15–2.03, respectively, suggesting partial synergy or indifference in the majority of strains. The combination of clarithromycin and metronidazole showed synergistic activity against 14 of 28 H. pylori strains tested. The in vitro activity results suggest the combination of fosfomycin with either amoxicillin or clarithromycin may be a promising alternative for the treatment of H. pylori infection. However, the clinical efficacy of these regimens remains to be investigated.     

Prevalence of resistant Helicobacter pylori isolates in Bulgarian children

The aim of this study was to assess the primary and combined resistances of Helicobacter pylori isolates obtained from paediatric patients in 2000-2001 to seven antimicrobial agents. Resistance rates of pre-treatment isolates from 115 children were investigated by the limited agar dilution method alone and by the E-test. The cut-off concentrations for resistance were: metronidazole >8 mg/L, clarithromycin and azithromycin >1 mg/L, clindamycin >4 mg/L, amoxicillin >0.5 mg/L, tetracycline >4 mg/L and ciprofloxacin >1 mg/L. Primary resistance rates were: metronidazole 15.8%, clarithromycin 12.4%, azithromycin 14.6%, clindamycin 20.0%, amoxicillin 0%, metronidazole + clarithromycin 4.5%, ciprofloxacin 6.0%, metronidazole + clarithromycin + ciprofloxacin 1.2%, tetracycline 3.1% and metronidazole + ciprofloxacin 1.2%. There were no significant age (1-9 years versus 10-18 years) or gender differences. Prevalence of both macrolide-resistant and intermediately susceptible strains was 21.9% for azithromycin and 15.9% for clarithromycin. Of 18 metronidazole-resistant isolates, 77.8% exhibited a metronidazole MIC > or = 32 mg/L. H. pylori resistance rates to metronidazole, clarithromycin and both agents were relatively low in Bulgarian children. However, resistance was found to all drugs tested except for amoxicillin. The consumption of newer macrolides and tetracyclines could be related to the prevalence of resistance to the corresponding agents. There were no significant differences in primary resistance rates of H. pylori to antimicrobial agents between children and adults except for metronidazole. Multi-drug resistance to newer macrolides, metronidazole and ciprofloxacin in association with a slightly elevated amoxicillin MIC (0.38 mg/L) was detected in one strain.     

Reevaluation of interpretive criteria for Haemophilus influenzae by using meropenem (10-microgram), imipenem (10-microgram), and ampicillin (2- and 10-microgram) disks.

A collection of 300 Haemophilus influenzae clinical strains was used to assess in vitro susceptibility to carbapenems (meropenem, imipenem) by MIC and disk diffusion methods and to compare disk diffusion test results with two potencies of ampicillin disks (2 and 10 micrograms). The isolates included ampicillin-susceptible or- intermediate (167 strains), beta-lactamase-positive (117 strains), and beta-lactamase-negative ampicillin-resistant (BLNAR; 16 strains) organisms. Disk diffusion testing was performed with 10-micrograms meropenem disks from two manufacturers. Meropenem was highly active against H. influenzae strains (MIC50, 0.06 microgram/ml; MIC90, 0.25 microgram/ml; MIC50 and MIC90, MICs at which 50 and 90%, respectively, of strains are inhibited) and was 8- to 16-fold more potent than imipenem (MIC50, 1 microgram/ml; MIC90, 2 micrograms/ml). Five non-imipenem-susceptible strains were identified (MIC, 8 micrograms/ml), but the disk diffusion test indicated susceptibility (zone diameters, 18 to 21 mm). MIC values of meropenem, doxycycline, ceftazidime, and ceftriaxone for BLNAR strains were two- to fourfold greater than those for other strains. The performance of both meropenem disks was comparable and considered acceptable. A single susceptible interpretive zone diameter of > or = 17 mm (MIC, < = or 4 micrograms/ml) was proposed for meropenem. Testing with the 2-micrograms ampicillin disk was preferred because of an excellent correlation between MIC values and zone diameters (r = 0.94) and superior interpretive accuracy with the susceptible criteria at > or = 17 mm (MIC, < or = 1 microgram/ml) and the resistant criteria at < or = 13 mm (MIC, > or = 4 micrograms/ml). Among the BLNAR strains tested, 81.3% were miscategorized as susceptible or intermediate when the 10-micrograms ampicillin disk was used, while the 2-micrograms disk produced only minor interpretive errors (12.5%). Use of these criteria for testing H. influenzae against meropenem and ampicillin should maximize reference test and standardized disk diffusion test performance with the Haemophilus Test Medium. The imipenem disk diffusion test appears compromised and should be used with caution for detecting strains for which imipenem MICs are elevated.     

Fluconazole disk diffusion procedure for determining susceptibility of Candida species.

A simple disk diffusion test was defined for quick determination of the susceptibility of Candida species to fluconazole. The standard macrotube dilution reference method, the fluconazole E test, and a 25-microgram fluconazole disk test were all performed with each of 250 Candida species selected to provide a broad range of fluconazole MICs. All three methods were in excellent agreement. On RPMI 1640-glucose agar, isolates with inhibition zone diameters of > or = 19 mm were all susceptible (MIC, < or = 8.0 micrograms/ml) by the E test and 94% were susceptible by the macrotube method. Strains with smaller zones were either resistant, intermediate (dose-dependent susceptibility), or susceptible by the reference methods. The disk test did not adequately separate fully resistant strains from those with dose-dependent susceptibility: additional quantitative tests are needed for the few strains that are not unequivocally susceptible by the disk method.     

Multicenter study of ofloxacin activity on bacteria isolated from a hospital environment

Minimal inhibitory concentrations (MICs) of ofloxacin were evaluated by agar dilution for 1508 bacterial strains isolated in five hospitals. For Enterobacteriaceae sensitive to nalidixic acid, MICs ranged from 0.008 to 1 microgram/ml (mode MIC: 0.12); the different species of Enterobacteriaceae exhibited similar mode MICs (0.12) with the exception of E. coli (0.06-0.12), P. mirabilis (0.5) and Providencia (0.25). Among strains intermediate and resistant to nalidixic acid, most of which were Serratia, Providencia and Citrobacter, 41% had a MIC within the susceptibility range, while the others had a MIC of 2 to 8 micrograms/ml, or even 64 micrograms/ml in a few instances. Ofloxacin also exhibited satisfactory activity against P. aeruginosa, with MICs ranging from 0.25 to 16 micrograms/ml (mode MIC: 2) for 87% of strains, and A. calcoaceticus, with MICs from 0.25 to 2 micrograms/ml (mode MIC: 1). Haemophilus sp. (MIC: 0.008 to 0.06 microgram/ml; mode MIC: 0.03), Gonococci (mode MIC: 0.008), and Meningococci (mode MIC: 0.016) were very sensitive to ofloxacin. The spectrum of ofloxacin included Gram positive cocci: MICs of Staphylococci were 0.06 to 2 micrograms/ml (mode MIC: 0.5); Enterococci, other Streptococci and Pneumococci were less sensitive, with MICs of 2 to 4 micrograms/ml for the majority of strains. As for anaerobic bacteria, ofloxacin proved more active against Clostridium (0.5 to 2 micrograms/ml) than Bacteroides (0.5 to 16 micrograms/ml).